Electrical flame ignition and supervising apparatus



March 11, 1969 3,432,246

ELECTRICAL FLAME IGNITION AND S'UPERVISING APPARATUS K. J. H ALLGREENFiled March 2, 1967 United States Patent 1) 49,515 US. Cl. 431-27 rm.c1. F23n /08 4 Claims ABSTRACT OF THE DISCLOSURE Flame ignition andsupervisory apparatus for use in conjunction with a burner and a sourceof fuel to the burner provided with an electrical ignition element forigniting fuel discharged from the burner and monitoring the existence ofa flame at the burner once the burner is ignited. Ignition control andsupervisory circuitry are connected to the element to electricallyenergize it and render it incandescent and continually electricallyenergize it while flame continues to burn at the burner. The burner isdisposed to monitor the flame and the control and supervisory circuitrycontrols an electromagnetically actuated valve controlling applicationof the fuel to the burner upon energization of the element anddiscontinuing supply of fuel to the burner when the element isdeenergized in response to the absence of a flame.

This invention relates generally to gas or oil fired burner ignition andcontrol and more particularly to electrical flame ignition andsupervisory apparatus.

Combined ignition and flame supervising apparatus are known. These knowndevices make use of a high voltage ignition spark path which comprisesan ion rectifier which carries out flame ignition and supervision andmonitoring after ignition. The known apparatus, however, are relativelycostly because of the necessity of using a high voltage transformer inthe circuitry. Moreover, these known apparatus have a limitation in thatan AC power source must be available. Furthermore, the ignition ele-.ments are rather sensitive to contamination and fouling.

The present invention has a principal object provision of a flameignition and supervisory apparatus for igniting a flame at a burner andmonitoring the fuel supply thereto by monitoring the flame.

Another object is to provide apparatus which is less expensive and moretroublefree and is capable of operating with alternating or directcurrent.

A feature of the invention is the provision of an electrical ignitionelement rendered incandescent for igniting a fuel at a burner andcomprising a material with a negative temperature coefiicient ofelectrical resistance. The ignition element is maintained in circuitwith ignition circuitry and supervisory or control circuitry continuingthe monitoring of a flame after ignition and turning off supply of fuelupon the absence of a flame.

The incandescent ignition element conducts an electrical currentcorresponding to its cold resistance when energized under control of amain switch, for example a boiler thermostat, and upon energization itsresistance decreases so that within a short time current flowtherethrough renders the material incandescent. So long as the ignitedflame burns, a large current flows in the supervisory circuit ormonitoring circuitry to which the ignition element is connected uponignition of the fuel. Should the flame become extinguished, a currentdrop takes place in the supervisory circuitry due to an increase inresistance of the super- 3,432,246 Patented Mar. 11, 1969 visoryignition element and supply of fuel is cut off to the burner.

Another feature of the invention is the provision of ignition or firingcircuitry for initially energizing the ignition element and controllingsupply of fuel to a burner and subsequently automatically changing overto supervisory control circuitry application of current at a reducedvalue so long as a flame obtains at the burner. A relay is connected inthe circuitry, maintaining fuel supply to the burner while energizedwith the reduced value of current corresponding to a holding current.

The firing and supervisory circuitry comprises a safety trip fordeenergizing the ignition element after a predetermined number ofignition attempts at igniting a fuel fail. The safety trip compriseselements to protect a fuel supply motor against overcurrent or shortcircuiting.

Other features and advantages of the ignition and flame supervisoryapparatus in accordance with the present invention will be betterunderstood as described in the following specification and appendedclaims, in conjunction with the following drawings in which:

FIG. 1 is a schematic diagram of a first embodiment of ignition andsupervisory apparatus in accordance with the invention; and

FIG. 2 is a second schematic diagram of a second embodiment of theapparatus in accordance with the invention.

As illustrated in the drawings, a motor driven pump 1 provides fuel, forexample oil from a fuel supply source, not shown, through a dischargeline 2 to an electromagnetically controlled valve 3 connected to aburner or nozzle 4 illustrated diagrammatically. The fuel is ignited atthe burner which burns as a flame 5. Ignition of the fuel is carried outby an ignition and resistanc element 6 made for example in the form of aU-shaped thin rod of silicon carbide granules bonded by siliconoxy-nitride. This material is supplied, for example by NortonInternational Inc. under the trade name Chrystolon 63 Silicon Carbideand distributed as a refractory lining material for furnaces.

The ignition or resistance element 6 is connected across terminals 7, 8of a 220 V. AC. main network through a first circuit comprising a mainswitch, for example a boiler thermostat switch 9, a movable contact 10of a safety trip 11 and a rectifier 12 connected in series with anoperating coil 13 of a relay 14 having a capacitor 15 in parallel withthe operating coil 13 and in series with a movable contact 16 of therelay 14. This first described circuitry coustitutes an ignition circuitfor electrically energizing the ignition element 6 to ignite the flame 5as hereinafter described.

A second or supervisory circuit is connected to the ignition element 6and includes the elements of the first described circuit and a shunt 17having a variable resistor 18 connected across movable contact 16 of therelay 14.

A third supervisory circuit branch comprises a directaction heater 19 inthe safety trip 11 in series with a variable resistor 20 and a secondmovable contact 21 of the relay 14. This last described circuit isconnected to the element 6 through the relay contact 21 in series withthe contact 10 of the safety trip 11 so that when the first describedcircuitry is energized, the relay 14 is actuated and the contact 16opens the first circuit so current flow is through the shunt while thecontact 21 closes a third set of stationary contacts closing a fourthbranch circuit to the ignition element 6 through an operating coil 22for operating the electromagnetic valve 3 and in series with anindirect-action resistor heater 23.

When the main or thermostatic switch 9 is closed, current energizes thefirst circuit including the relay coil 13 and the elements 6 and in thethird circuit, the heater 19 and the element 6. The ignition element 6is rendered incandescent as the current passing therethrough rises dueto the decreasing resistance thereof. As soon as this current hasobtained a level which renders the element 6 completely incandescent,the current corresponds to the necessary operating current level foractuating the relay 14. As the relay 14 is actuated, the current throughthe heater 19 is interrupted by the contact 21 and the current valuethrough the relay coil 13 is reduced in view of the placing of theresistor 18 in the shunt 17 in circuit upon opening of the contact 16.

With the shunt in circuit the current in the relay coil 13 is suificientto act as holding current for the relay 14 but current flow isinsufficient to continue to maintain the ignition element 16incandescent. When the relay is energized, the circuit of coil 22 isclosed so it is energized and the electromagnetic valve 3 is operatedfrom a closed position to an open position so that fuel is delivered tothe nozzle or burner 4 by the motor driven pump 1 which is continuouslyenergized through the indirect action resistor heater 23 and is alwaysin circuit with ignition and supervisory element 6 once the main switch9 is closed.

When the valve 3 opens the ignition element is incandescent. If the fuelfails to ignite properly, the flame is extinguished and the ignitionelement 6 cools down to a temperature at which its inner resistancebecomes sufficiently large that the current flow therethrough fallsbelow the holding current level for relay 14 and the relay 14 drops out.When the relay drops out, the ignition circuit or first circuit is againclosed and a second attempt at ignition in the above described mannertakes place.

During each attempt at ignition, the heater 19, which may consist of aheating wire directly wound on a bimetal strip, generates apredetermined amount of heat and stores it, consequently the temperatureand heat content thereof rise until finally the heater will open themovable contact and trip the safety trip 11. The resistor is variableand is used to set the value at which the heater 19 will trip the relayand therefore the number of ignition attempts that the ignitioncircuitry can attempt.

In the event that the motor driven pump 1 is overloaded, for example ifit should become frozen or blocked, the second heater 23 will radiatesuflicient heat to actuate the heater 19 and cause it to trip the safetytrip 11 thus protecting the motor and the valve coil 22 against shortcircuits and the like.

The variable resistor 18 enables the holding current of relay 14 to beset at a desired value and allows adapting the characteristic parametersof the ignition element 6 to the parameters of the relay 14.

A second embodiment of apparatus in accordance with the invention isillustrated in FIG. 2 in which the elements corresponding to theapparatus in FIG. 1 have similar reference numerals. In this embodiment,the circuitry is connected substantially the same except that theelectromagnetic valve 3 is replaced by an electromagnetic valve 24operated by an operating coil 25 constituting the operating coil of arelay 26 replacing the relay 14 of the first embodiment. The relay isprovided with movable contacts 27, 28 which are normally closed in amanner of the contacts 16, 21 of the relay 14. The circuitry functionsin the manner of the first embodiment except that instead of a delaytaking place in the opening of the fuel valve 24 as in the other valve 3the valve 24 is immediately actuated to an open position when theoperating coil 25 is electrically energized and operates the contacts27, 28 to their open position in which current flow to the ignitionelement 6 is through the shunt 17.

In this instance, ignition is effected by the ignition element 6 beingheated to its incandescent state by current flow through the coil 25 andthe shunt 17. When the relay is energized, current flow through theelement 6 is reduced by means of the resistor 18 in the shunt 17 to avalue corresponding to the holding current for holding the relay 26. Thesafety trip 11 in this embodiment will likewise be triggered whenseveral ignition attempts fail: to produce a flame or in the event thatthe motor runs with an overcurrent therein.

A number of modifications can be carried out in both embodiments withoutdeparting from the concepts of the invention. Thus, the fuel source neednot comprise a motor driven pump 1 but may be, for example, a remotesupply of fuel under pressure, for example a pressure gas fuel sourcefor a gas fired burner. Moreover, the coil 22 of the electromagneticvalve may be connected without protection by the safety device or trip11. The relays for cutting off ignition current may be provided withselfholding contacts, not shown, whose current does not pass through theignition element 6 and may also remain permanently disconnected untilreset manually.

Those skilled in the art will understand that the terminology firstcircuit, second circuit and third circuit etc. are terms used for easeof description and are not indicative of the number of necessarycircuits for carrying out the principles of the invention.

While preferred embodiments of the invention have been shown anddescribed, it will be understood that many modifications and changes canbe made within the true spirit and scope of the invention.

What I claim and desire to be secured by Letters Patent 1. Flameignition and supervisory apparatus for use in conjunction with a burnerand a source of fuel to said burner comprising, an electricallyenergized ignition and supervisory resistance element for igniting fueldelivered from said burner and monitoring the presence and absence of aflame at said burner, said element having a negative temperaturecoefiicient of electrical resistance, circuit means comprising anignition circuit connectable to said element energizing said element toheat it to a temperature igniting said fuel from said burner and asupervisory circuit comprising a part of said energizing circuitconnect-able to said element to continue said element electricallyenergized during presence of said flame, said element being disposed tosense the pressure and absence of said flame, a current-responsive relayhaving contacts common to said ignition circuit and said supervisorycircuit in series with said element for alternatively connecting saidelement to said ignition circuit and said supervisory circuit, anelectromagnetic valve having a coil connected in said circuit means inseries with said element through said contacts connected to be energizedby said ignition circuit to open said valve and to retain said valveopen under control of said element, a holding circuit for said relayshunting said contacts and in series with said element when saidcontacts open and rendered effective when said relay is energized andsaid. contacts open, a variable resistor in said holding circuit inseries with said element when said holding circuit is renderedeffective, whereby current value in said holding circuit is undercontrol of said element and the resistance of said resistor and saidrelay drops out when said current drops below a selected value inresponse to rise of the resistance of said element above a selectedvalue, and safety trip means common to said ignition circuit and saidsupervisory circuit connected to said element through said contactseffective to deenergize said coil to cut-off fuel to said burner and todeenergize said element when there has been extinguishment of said flameat said burner and in response to said element causing said relay toalternatively connect said ignition circuit and said supervisory circuitto said element without ignition of said fuel.

2. Flame ignition and supervisory apparatus, according to claim 1, inwhich said coil is connected common to said valve and said relay foroperating said valve and said relay.

3. Flame ignition and supervisory apparatus according to claim 1, inwhich said relay comprises a coil in 5 6 series with the contacts ofsaid relay rendering said hold- 2,068,425 1/ 1937 McCabe. ing circuitelfective. 2,159,658 5/ 1939 Hall 15 8 -12 4. Flame ignition andsupervisory apparatus according 2,887,152 5/1959 Wilder.

to claim 1 in which said safety trip means is connected 3,209,80910/1965 Nielsen et al.

in series with contacts of said relay other than contacts 5 3,282,32411/1966 Romanelli 158-12( of said relay rendering said holding circuitefiective.

JAMES W. WESTHAVER, Primary Examiner. References Cited U's CL UNITEDSTATES PATENTS 431 66 1,745,178 1/1930 McCabe. 10

